Hello Danny,I would like to as what if I redirect my old domain to an existing domain?

I had 2 domains, and decided to merge them, so redirected domain A.com to domain B.com, and now I see an awful drop in SERP for domain B.com.Is there anything i should do? Like it's better to keep both domains?Or i should just wait for the SERP to come back to it's usual positions? (As I think if i failed it can never happen)